In the automobile industry, as general concerns about energy and environment are increased globally, the efficiency in each part including fuel efficiency has been steadily improved, and the external appearance of a vehicle has been also diversified in order to satisfy various demands of customers. According to such a tendency, research and development on lighter weight, smaller size and multi-function of each vehicle component has been carried out. Particularly, in an air-conditioning unit for a vehicle, since it is generally difficult to secure an enough space in an engine room, there have been many efforts to manufacture a heat exchange system having a small size and high efficiency.
Meanwhile, the heat exchange system generally includes an evaporator for absorbing heat from a peripheral portion, a compressor for compressing refrigerant, a condenser for radiating heat to a peripheral portion, and an expansion valve for expanding the refrigerant. In an air-conditioning system, the gaseous refrigerant introduced from the evaporator to the compressor is compressed at a high pressure and high temperature, and the compressed gaseous refrigerant radiates liquefaction heat to a peripheral portion while passing through the condenser so as to be liquefied, and the liquefied refrigerant is passed through the expansion valve so as to be in a low pressure low temperature wet vapor state and then introduced again into the evaporator so as to be vaporized, and thus the air conditioning substantially occurs in the evaporator that absorbs vaporization heat from a peripheral portion while the wet vapor refrigerant is vaporized. As described above, the condenser and evaporator in the air-conditioning system typically fall into the category of the heat exchanger.
FIG. 1 is a perspective view of a general heat exchanger. As shown in the drawing, the heat exchanger 100 includes a pair of header-tanks 10, a plurality of tubes 20 and a plurality of fins 30. The header-tank 10 includes a plurality of tube insertion holes 13 that are formed at a lower surface or an upper surface thereof to be extended in a width direction thereof and arranged in a longitudinal direction thereof, an end cap 14 that closes both longitudinal ends thereof, at least one partition wall 11 that partitions an inner space as a refrigerant passage in the longitudinal direction and at least one baffle 12 that partitions the refrigerant passage in the width direction. Further, both ends of the tube 20 are fixedly inserted into the tube insertion hole 13 of the header-tank 10 to form a refrigerant passage, and the fin 30 is interposed between the tubes 20 to enhance heat exchange performance.
FIG. 2 shows a flow of the refrigerant in the heat exchanger as described above, wherein FIG. 2A is a schematic view of the heat exchanger to shown the refrigerant flow indicated by an arrow, and FIG. 2B is a schematic view showing the refrigerant flow in a status that each row of the hear tanks 10 arranged in two rows is separated from each other and the tubes are omitted. As shown in the drawing, in a first row 10b1 of lower header-tank and a second row 10b2 of lower header-tank, the refrigerant passage is partitioned by the baffle 12. First, the refrigerant introduced into a front space of the baffle 12 is flowed into a first row 10a1 of upper header-tank through the tube 20. Because the refrigerant is introduced through only one side of the first row 10a1 of upper header-tank, the refrigerant introduced into the first row 10a1 of upper header-tank is flow to the other side, i.e., an empty space in a direction indicated by an arrow, and then introduced into a rear space of the baffle 12 in the first row 10b1 of lower header-tank through the tube 20.
The first row 10b1 of lower header-tank and the second row 10b2 of lower header-tank are communicated with each other through a communication hole 15′ formed at the rear space of the baffle 12, and thus the refrigerant introduced into the first row 10b1 of lower header-tank is flowed through the communication hole 15′ to the rear space of the baffle 12 in the second row 10b2 of lower header-tank. Then, the refrigerant is exhausted to an outside through the rear space of the baffle 12 in the second row 10b2 of lower header-tank, a second row 10a2 of upper header-tank and the front space of the baffle 12 in the second row 10b2 of lower header-tank.
However, in the heat exchanger having the refrigerant flow as described above, there has been many problems in designing the communication hole. There has been disclosed Japanese Patent Publication No. 2002-071283 (hereinafter, called “conventional invention”) relevant to the design of the communication hole. FIG. 3 shows a cross-sectional view and a perspective view of a heat exchanger according to the conventional invention. As shown in the drawing, in the conventional invention, one communication hole is formed at one tube. However, if one communication hole is formed at one tube, a structure of the heat exchanger is complicated due to many holes, and manufacturing cost is increased. Also, since there is a high possibility of generating a dead zone due to non-uniformity of the refrigerant flow, a temperature distribution is non-uniform and thus the heat exchange performance is deteriorated. Further, there is an inconvenience in that the communication hole should be redesigned according to the standard of the fin. Furthermore, since the communication hole is formed at every tube, durability is considerably reduced.